Catalytic cyclohexane oxidation to KA oil using novel hydrosoluble copper(I) complexes bearing aminophosphine ligands: Water as a selectivity promoter

Reacting the alkylated 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane (PTA), namely (PTA-CH₂-C₆H₄-p-COOH)Br (1) or (PTA-CH₂-C₆H₃-p-OH-m-CHO)Cl (2), with CuBr, CuI or [Cu(CH₃CN)₄]BF₄, under mild conditions using different stoichiometric ratios resulted in the formation of the new water soluble copper complexes [CuBr₂(PTA-CH₂-C₆H₄-p-COOH)₂]X (X = Br {3a}, I {3b} or BF₄ {3c}), [CuBr(PTA-CH₂-C₆H₄-p-COOH)₃]Br₃ (4) and [CuCl₂(PTA-CH₂-C₆H₃-p-OH-m-CHO)₂]X (X = I {5a} or Cl {5b}). The compounds were characterized using multinuclear NMR, FTIR, ESI-MS and elemental analysis. The molecular structure of the neutral form of 3 was established by single crystal X-ray diffraction. In a homogeneous aqueous medium, the catalytic activity of the hydrophilic complexes was assessed for the cyclohexane oxidation to the KA oil (a mixture of cyclohexanone and cyclohexanol). The selectivity towards cyclohexanone is controlled by water, increasing with the H₂O amount, and becoming higher than that of cyclohexanol for the 25–75% range of water in the solvent composition. Complex 5a exhibited the highest catalytic activity, achieving up to 21% conversion after 4 h at 50 °C using 0.5 mol% of the catalyst. Utilizing a similar loading of 5a, under microwave irradiation, afforded 18% of yield after 1.5 h at 70 °C.